Natural fiber welded (NFW) yarns embedded with porous carbon ­materials are described for applications as electrodes in textile electrochemical capacitors. With this fabrication technique, many kinds of carbons can be embedded into cellulose based yarns and subsequently knitted into full ­fabrics on industrial knitting machines. Yarns welded with carbon and ­stainless steel have device capacitances as high as 37 mF cm‐1, one of the highest reported values for carbon‐based yarns. The versatility of this ­technique to weld any commercially available cellulose yarn with any ­micro‐ or nanocarbon means properties can be tuned for specific applications. Most importantly, it is found that despite having full flexibility, increased strength, and good electrochemical performance, not all of the electrode yarns are ­suitable for knitting. Therefore, it is recommended that all works reporting on fiber/yarn capacitors for wearables attempt processing into full fabrics.

A process we term “natural fiber welding” is demonstrated by which loose fibers are transformed to create a congealed network using an IL solvent. Several examples are discussed that include cellulosic and protein‐based materials. SEM shows the fusion of fibers upon treatment. XRD and FT‐IR spectroscopy of cellulosic materials show that significant amounts of the native polymer structure are retained after the process is completed. Data suggest that material at the fiber exterior is preferentially transformed while material in the fiber core is left in the native state. Data also demonstrate that the amount of material modified can be tailored by control of variables such as the IL solvent concentration, the process temperature, and the processing time.

A systematic study of variables that affect the fiber welding process is presented. Cotton cloth samples are treated with controlled amounts of 1-ethyl-3-methylimidazolium acetate for a series of times and temperatures. Diluting the ionic liquid with a volatile molecular co-solvent allows temporal and spatial control of the welding process not possible with neat ionic liquids. Materials are characterized by scanning electron microscopy, infrared spectroscopy, X-ray diffraction, and mechanical (tensile) testing. Results suggest careful management of process variables permits controlled, reproducible manipulation of chemical and physical properties.

In our study, lignocellulose yarns were fabricated via natural fiber welding (NFW) into a robust, free-standing, sustainable catalyst for water treatment. First, a series of powder catalysts were created by loading monometallic palladium (Pd) and bimetallic palladium−copper (Pd−Cu) nanoparticles onto ball-milled yarn powders via incipient wetness (IW) followed by a gentle reduction method in hydrogen gas that preserved the natural fiber while reducing the metal ions to their zerovalent state. Material characterization revealed Pd preferentially reduced near the surface whereas Cu distributed more uniformly throughout the supports. Although no chemical bonding interactions were observed between the metals and their supports, small (5−10 nm), near-spherical crystalline nanoparticles were produced, and a Pd−Cu alloy formed on the surface of the supports. Catalytic performance was evaluated for each Pd-only and Pd−Cu powder catalyst via nitrite and nitrate reduction tests, respectively. Next, the optimized Pd−Cu linen powder catalyst was fiber-welded onto a macroporous linen yarn scaffold via NFW and its catalyst performance and reusability were evaluated. This fiber-welded catalyst reduced nitrate as effectively as the corresponding powder, and remained stable during five consecutive cycles of nitrate reduction tests. Although catalytic activity declined after the fiber-welded catalyst was left in air for several months, its reactivity could easily be regenerated by thermal treatment. Our research highlights how lignocellulose supported metal-based catalysts can be used for water purification, demonstrating a novel application of NFW for water treatment while presenting a sustainable approach to fabricate functional materials from natural fibers.

The utilization of ionic liquids (ILs) for future electrochemical applications shows great promise. Recently ILs have been investigated for many electrochemical systems however, further characterization and development of ILs remains as they are utilized in devices such as batteries, capacitors, fuel cells, sensors, and other applications. In this study, we present time resolved (TRS) FTIR spectroscopy data as a means to characterize interfaces between IL-based electrolytes and gold electrodes. These data are important in that dynamic interactions at the electrode/electrolyte interface are crucial to device efficiency, power density, sensitivity, et cetera.